Autism is currently widely viewed as a spectrum disorder with affected individuals having varying degrees of social and emotional disturbances. In the present application we describe a new conceptualization of autism in order to account for some of the heterogeneity. In the application, a neuroendocrine spectrum model is proposed in which aspects of emotional reactivity, social responsiveness and biological indices intersect to define distinct subtypes. The investigation involves three interrelated studies of socioemotional functioning utilizing several methods of analysis to include the assessment of biological markers of emotional arousal and stress, sophisticated behavioral observational techniques, and functional neuroimaging in order to carefully explore the psychobiological profiles of children with and without autism. Specifically, during peer interactions of a playground activity, sophisticated behavioral observation will be obtained to evaluate the frequency, duration and interactive sequences exhibited by children with autism. These data will be analyzed with stress hormones to uncover relationships between behavioral and biological symptom profiles. In addition, we will explore brain activation patterns in these children while they play games with different computer and human partners. It is anticipated that this comprehensive study of real world social interactions will allow us to uncover meaningful associations between the child's behavior, biological profiles and brain activity before, during and after play with peers. The ultimate goal is that these results will better inform our understanding of autism to allow us to provide individualized biological and behavioral treatments.